Find the domain and range of the curve x^2+y^2-6x+8y+21=0?

This topic has always been one of my weaker areas in maths and I'm struggling to figure out this answer...

* Find the domain and range of the curve x^2+y^2-6x+8y+21=0

From this question, I've done some working and found the curve also to be equal to:(x-3)^2 + (x+4)^2 = (2)^2

I found the above by using the Completing the Square method, but I don't
know if I'm even going about this the right way or not - any help in
answering this question would be Greatly Appreciated!! Thanks in advance
to anyone who can help! :)